Electronic camera apparatus with facility for varying size or position of a focus detecting frame in focus control

ABSTRACT

Each time an area of a distance measurement frame is changed at a position near the center of the lens focused position of a lens unit between the infinite range and the shortest range, a value of a high frequency component which is independent on a contrast is calculated by a system control circuit by a high frequency component in the distance measurement frame which is obtained from a high-pass filter and a luminance component which is obtained from an integrator. The calculated value is compared with a reference value by the system control circuit. When the calculated value is equal to or smaller than the reference value as a result of the comparison, the distance measurement frame is enlarged at a predetermined ratio by the system control circuit. On the other hand, when the calculated value exceeds the reference value, a signal is supplied to a lens driving motor from the system control circuit in accordance with an ES value which is obtained through an ES filter from the inside of the distance measurement frame and the lens unit is moved by the lens driving motor, thereby executing a focus adjustment.

This is a division of application Ser. No. 08,490,312, filed Jun. 14,1995, U.S. Pat. No. 5,565,917 which is a continuation of Ser. No.07/950,444, filed Sep. 22, 1992, abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an electronic camera having an automatic focusadjusting apparatus.

2. Related Background Art

Almost all of the recent cameras have the automatic focus adjustingfunction irrespective of the types of the cameras.

FIG. 1 is a block diagram showing a construction of such a kind ofelectronic camera.

In FIG. 1, reference numeral 1 denotes a lens unit; 2 a lens drivingmotor; 3 an iris; 4 an iris driving circuit; 5 a solid-state imagepickup element such as a CCD or the like for converting an object imageinto an electric signal; 6 a solid-state image pickup element drivingcircuit to drive the solid-state image pickup element; 7 an A/Dconversion circuit for A/D converting an image pickup signal generatedfrom the image pickup element 5 into a digital signal; 8 a memory tostore an output digital signal of the A/D conversion circuit 7; 9 an ESfilter to calculate an ES value (which will be explained hereinlater)indicative of a blur amount from the image pickup signal stored in thememory 8; 10 a system control circuit to control the whole system of theelectronic still camera; 11 an image pickup signal processing circuitfor executing processes such as gamma (γ) conversion, band limitation,and the like to the output of the memory 8; 12 a D/A conversion circuitto D/A convert a digital output signal of the image pickup signalprocessing circuit 11 into an analog signal; 13 a frequency modulationcircuit to frequency modulate an output of the D/A conversion circuit12; 14 a recording amplifier to amplify an output current of thefrequency modulation circuit 13; 15 a magnetic head; 16 a magnetic sheetas a recording medium; 17 a motor to rotate the magnetic sheet 16; 18 amotor servo circuit to stabilize the rotation of the motor; 19 aphotometry element to measure the brightness of the object; and 20 arelease switch. A series of photographing operations are started byturning on the release switch 20.

FIG. 2 shows a construction of the image pickup element 5 shown in FIG.1.

In FIG. 2, reference numeral 501 denotes an interline transfer typesolid-state image pickup element; 502 a photodiode for converting thelight into the charges and accumulating; 503 a vertical CCD tovertically transfer the charges generated in the photodiode; and V₁ toV₄ transfer electrodes of the vertical CCD 503. The transfer electrodeV₁ also functions as a transfer gate to transfer the charges of theodd-number rows of the photodiode. Similarly, the transfer electrode V₃also functions as a transfer gate to transfer the charges of theeven-number rows of the photodiode. The vertical CCD 503 is driven bytransfer pulses of four phases. Reference numeral 504 denotes ahorizontal CCD to horizontally transfer the charges which aretransferred from the vertical CCD 503; and H₁ and H₂ indicate transferelectrodes of the horizontal CCD 504. The transfer electrodes H₁ and H₂are driven by transfer pulses of two phases. Reference numeral 505denotes an output amplifier for converting the charges into the voltageand generating; 506 a top drain to drain the unnecessary charges by thereverse transfer; and 507 a bottom drain to drain the unnecessarycharges by the forward transfer.

FIG. 3 shows an operation sequence of the electronic still camera withthe automatic focusing function. When the release switch 20 is turned onat a time T₀, a series of photographing sequence is started. The optimumiris value A_(v) and the optimum shutter speed T_(v) are calculated fromthe output of the photometry element 19. The iris is set into an openstate for a period of time between T₁ and T₂. The lens unit 1 is movedby the lens driving motor 2 to the focusing position in a range from theinfinite range to the shortest range in an n-stage step manner orcontinuously for a period of time between T₂ and T₃. A series ofoperations such as draining of unnecessary charges, exposure, andreading of the signal charges of n times, that is, the AF operation isexecuted. The blur amount is calculated from the output of thesolid-state image pickup element 5 in the reading operations of thesignal charges of n times, thereby calculating the position of thesmallest blur amount, namely, the optimum focus position. The iris valueis set to A_(v) for a period of time between T₃ and T₄ and the lens unit1 is set to the focused lens position. The clearing operation to drainthe unnecessary charges to the top drain 506 by the reverse transfer isexecuted from a time T₄. After that, the regular exposure is performed.Subsequently, the signal charges are read out from a time T₅ and theprocessed signal is recorded onto the magnetic sheet 16.

FIG. 4 is a diagram for explaining one of the methods of detecting theES value (edge spread value) indicative of the blur amount (hereinafter,referred to as an ES method). Since the ES value and the ES method havebeen disclosed in U.S. Pat. No. 4,804,831, they will be merely simplyexplained here. As shown in FIG. 4A, the edge of the video signalsharply rises in the focused state and slowly rises in the unfocusedstate. FIG. 4B shows an absolute value D of the differential waveform ofthe video signal. FIGS. 4C and 4D show delay signals DL₁ and DL₂ of thedifferential waveform D, respectively. FIG. 4E shows an integralwaveform I and indicates a contrast of the edge portion of the videosignal. FIG. 4F shows the ES value indicative of a sharpness of the edgewhich is obtained by dividing D by I.

FIG. 5, shows an example of a construction of the ES filter 9.

In FIG. 5, reference numeral 801 denotes a differential circuit; 802 anabsolute value circuit; 803 a delay circuit; 804 an integral circuit;805 a division circuit; 806 a peak-hold circuit. The value having thelargest ES value in the image information is determined to be an ESvalue of the object.

FIG. 6 shows changes in lens position and ES value when the AF operationis executed in order to obtain the in-focus position.

The lens is continuously conveyed from the minimum position to themaximum position. During the lens conveyance, the image information isaccumulated into the solid-state image pickup element 5 every verticalscan period (hereinafter, abbreviated to 1 V). The accumulated imagesignal is read out and the ES value is obtained from the read-out imageinformation. The position of the largest ES value is determined to bethe in-focus position. An axis of abscissa indicates a lens travelingamount. An axis of ordinate indicates a focusing signal (in this case,ES value). A curve in which the focusing position that is drawn in thisinstance is set to the peak point is called a mountain climbing curve.The mountain climbing curve according to the ES method is steep and ahigh focus detecting precision is obtained. In the above description,the AF operation is executed by using all of the image information whichis supplied. However, since a high processing speed is required in theAF operation, a distance measurement frame having a predetermined areais ordinarily used and the AF operation is performed within the distancemeasurement frame.

However, since the area of the distance measurement frame is fixed to apredetermined value in the conventional AF operation, for instance, inthe case where the distance measurement frame has a wide area as shownin FIG. 7A, for example, when both of a tree of a remote range and a manof a near range are simultaneously located in the distance measurementframe, a plurality of peaks exist in the ES value shown in the diagram.The AF operation is, therefore, unstable with respect to a point thatthe focal point is set to which one of the peak positions. On thecontrary, in the case where the distance measurement frame has a narrowarea as shown in FIG. 7B, in many cases, a high frequency component tofind out the focal point is not included in the distance measurementframe. The ES value is small. In the worst case, there is a problem suchthat no peaks exists in the ES value and the accurate AF operation isnot performed.

SUMMARY OF THE INVENTION

It is the first object of the invention to provide an electronic stillcamera which can solve the foregoing problems and can execute theaccurate AF operation.

The second object of the invention is to provide an electronic camera inwhich an AF system using a video signal can be applied to an electronicstill camera.

The third object of the invention is to provide an electronic camerawhich can always accurately set a focal point to an object withoutcausing an erroneous operation such as perspective competition or thelike irrespective of the state of an object.

To accomplish the above objects, according to a preferred embodiment ofthe invention, there is provided an electronic camera comprising:distance measurement frame setting means for changing an area of adistance measurement frame; arithmetic operating means for extracting apredetermined signal component in the distance measurement frame and forconverting into a predetermined signal which is independent of acontrast; and a focus control means which is constructed in a mannersuch that an output level of the arithmetic operating means is comparedwith a reference level, when the output level is equal to or lower thanthe reference level, the distance measurement frame setting means iscontrolled so as to enlarge the area of the distance measurement frameat a predetermined ratio, and when the focusing signal level is higherthan the reference level, the focusing operation is executed within thedistance measurement frame.

According to another preferred embodiment of the invention, there isdisclosed an electronic camera comprising: arithmetic operating meansfor calculating a value of a high frequency component which isindependent of a contrast from the high frequency component and aluminance component in a distance measurement frame each time thedistance measurement frame is moved to a plurality of predeterminedpositions in accordance with a predetermined order; comparing means forcomparing the value calculated by the arithmetic operating means and areference value; moving means for moving the distance measurement frameto the next predetermined position in the case where the calculatedvalue is smaller than the reference value as a result of the comparisonby the comparing means; and focusing means for executing a focusingoperation in the distance measurement frame existing in the relevantposition in the case where the calculated value is larger than thereference value as a result of the comparison by the comparing means.

Consequently, it is possible to realize an automatic focus adjustingapparatus in which the optimum distance measurement frame can be setirrespective of a state of an object and it is always stable and a highprecision is obtained without causing an erroneous operation such asperspective competition or the like.

The above and other objects and features of the present invention willbecome apparent from the following detailed description and the appendedclaims with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an electronic still camera with anautomatic focusing function;

FIG. 2 is a diagram showing a construction of an interline transfer typesolid-state image pickup element 5 shown in FIG. 1;

FIG. 3 is a diagram for explaining an operating sequence of theelectronic still camera with the automatic focusing function;

FIGS. 4A to 4F are diagrams for explaining an ES method;

FIG. 5 is a block diagram showing a construction of an ES filter 9;

FIG. 6 is a diagram showing changes in the lens position and ES valuefor executing an AF operation;

FIGS. 7A and 7B are diagrams showing distance measurement frames when afocusing position is obtained;

FIG. 8 is a block diagram showing an embodiment of the invention;

FIG. 9 is a diagram for explaining an operating sequence of anelectronic still camera according to the embodiment;

FIG. 10 is a diagram showing an example of changes in the lens position,CU value, CU/Y value, and ES value when the focusing position isobtained;

FIG. 11 is a diagram showing an example of the movement of the distancemeasurement frame; and

FIG. 12 is a flowchart showing a photographing sequence of the wholeelectronic camera of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the invention will be described in detail hereinbelowwith reference to the drawings.

FIG. 8 shows an embodiment of the invention and relates to an example ofan electronic still camera with an automatic focusing function. In FIG.8, the same parts and components as those shown in FIG. 1 are designatedby the same reference numerals and their descriptions are omitted here.

In the diagram, reference numeral 101 denotes a high-pass filter todetect a high frequency component of an image. The filter 101 has broadfrequency characteristics in a movable range of a lens and a cut-offfrequency is set to a low value such that an output value is not equalto 0 even in the unfocused state, particularly, in a large blur state.An output of the filter 101 is referred to as a CU value. Referencenumeral 102 denotes an integrator to calculate a mean value of aluminance component of the image. An output of the integrator 102 iscalled a Y value.

Reference numeral 103 denotes a memory control circuit for making areading range from the memory 8 variable on the basis of a command ofthe system control circuit 10 when the image pickup signal stored in thememory 8 is read out and supplied to the ES filter 9, high-pass filter101, and integrator 102. That is, the memory control circuit 103controls the reading range in the image pickup picture plane of theimage pickup signal to be supplied to the ES filter 9, high-pass filter101, and integrator 102. In brief, the memory control circuit 103operates as a gate circuit to make a size and a position of the distancemeasurement frame variable. The image pickup signal which is read outfrom the memory 8 and supplied to the image pickup signal processingcircuit 11 is read out by an amount of the whole picture plane.Reference numeral 104 denotes an electronic view finder to monitor theimage which is generated from the processing circuit 11.

Display contents such as various control information, distancemeasurement frame, and the like are superimposed by a control signalfrom the system control circuit.

The focusing operation will now be described with reference to FIGS. 9and 10.

When the release switch 20 is turned on at the time T₀, a series ofphotographing sequence is started. The optimum iris value A_(v) and theoptimum shutter speed T_(v) are calculated from the output of thephotometry element 19. The iris is set to the open state for a period oftime between the times T₁ and T₂ and the lens unit 1 is moved to thefocus position near the center between the infinite range and theshortest range. The distance measurement frame of the minimum area whichcan be measured is set at the time T₂ and the first CU value and Y valueare calculated.

Even in case of the same high frequency component, the amplitudecharacteristic of the CU value differs in dependence on the luminancelevel. Therefore, for instance, by dividing the CU value by the Y valuein the system control circuit 10, the CU value can be normalized for theluminance, so that the high frequency component which is independent ofthe contrast can be extracted. The value of CU/Y is compared with anarbitrary reference value shown in FIG. 10. When the CU/Y value issmaller than the reference value as a result of the comparison, it isregarded that the distance measurement frame is small and no highfrequency component exists. The memory control circuit 103 is controlledby the system control circuit 10 and the area of the distancemeasurement frame is set to a slightly wide frame at a predetermined orarbitrary ratio. The CU value and Y value are again calculated andprocesses similar to the above processes are repeated until the value ofCU/Y exceeds the reference value.

When the value of CU/Y first exceeds the reference value, thecharacteristics of the ES value in which only one kind of peak(ES_(max)) by the ES method exists are obtained as will be understoodfrom FIG. 10. Therefore, the lens unit 1 is moved continuously or in ak-stage step manner to the lens position in a range from the shortestrange to the infinite range at the time T₃. Together with the movementof the lens unit 1, a series of operations such as draining of theunnecessary charges, exposure, and reading of the signal charges, thatis, the AF operation is executed. A blur amount is calculated through anES filter from an output of the solid-state image pickup element 5 inthe reading operation of the signal charges, thereby calculating theposition of the smallest blur amount, that is, an in-focus lens position(P) on the basis of an ES signal. Since the peak characteristic of theES value is set to one kind by adjusting the distance measurement framebefore the AF operation as compared with the conventional method, thestable and accurate AF operation can be performed. Further, bydisplaying the distance measurement frame into the electronic viewfinder of the camera, the AF operation can be more accurately executedto the object to be focused. The iris value is set to A_(v) for a periodof time between the times T₄ and T₅ and the lens unit 1 is set to thein-focus lens position (P). The clearing operation to drain theunnecessary charges to the top drain 506 by the reverse transfer isexecuted from the time T₄ -T₅. After that, the regular exposure isexecuted. The signal charges are subsequently read out from the time T₆and the processed signal is recorded onto the magnetic sheet 16.

A method of moving the distance measurement frame when a similar effectis obtained by moving the distance measurement frame instead of wideningthe distance measurement frame will now be described with reference toFIG. 11. The control itself can be performed by controlling the memorycontrol circuit 103 by the system control circuit 10 and by variablychanging the reading range from the memory.

First, the ratio of CU/Y is calculated with respect to the distancemeasurement frame (1). When the ratio is equal to or less than thereference value, the distance measurement frame is moved to the position(2) and operations similar to those mentioned above are executed. Afterthat, the distance measurement frame is moved in accordance with theorder of the reference numerals shown in FIG. 11 until the value of CU/Yis larger than the reference value. The AF operation based on the ESsignal is executed by using the distance measurement frame at a timepoint when the value of CU/Y exceeds the reference value. In this case,since the size of distance measurement frame is small, a time which isrequired to calculate the ES value or the like is short and thehigh-speed AF operation can be realized.

In the embodiment, when the lens unit 1 is moved to the in-focus lensposition (P) upon photographing, it is directly moved from the AFoperation end position. However, it is also possible to temporarily movethe lens unit 1 to the AF operation start position after completion ofthe AF operation and to subsequently move the lens unit to the P pointfrom the same direction as that in the AF operation.

The filter to detect the blur amount is not limited to the ES filterbut, for instance, a high-pass filter or a band-pass filter can be alsoused.

A band-pass filter can be also used as a filter 101 to detect the highfrequency component.

Further, although the embodiment has been described with respect to theexample in which the focus detecting means is constructed by the digitalfilter, the focus detecting means can be also realized in an analogmanner.

The whole photographing sequence will now be described.

FIG. 12 is a flowchart showing the photographing sequence of theelectronic camera in the invention. When the control is started, a checkis made in step S1 to see if the shutter release switch has been turnedon or not. The shutter release switch is constructed by strokes of twostages. The switch (1) is closed by the depression of the first stageand the switch (2) is closed by the depression of the second stage. Instep S1, a check is made to see if the first stage has been depressed ornot, namely, to see if the switch (1) has been turned on or not.

When the switch (1) is turned on in step S1, step S2 follows and aphotometry operation is executed and the iris value A_(v), the shutterspeed T_(v), and further a unit driving step number k of a focusing lenswhen performing the automatic focus adjusting operation are set. In stepS3, the iris is opened. After that, in step S4, the focusing lens ismoved to a position almost near the center between the shortest rangeand the infinite range. In step S5, the distance measurement framesetting operation is executed. The distance measurement frame settingoperation is as mentioned above. The operation to change the size orposition of the distance measurement frame is executed so that thesignal level in which the high frequency component in the image pickupsignal has been normalized by the mean value of the luminance signal isequal to or higher than the reference level.

After completion of the distance measurement frame setting operation, instep S6, the focusing lens is actually driven on a k-step unit basiswhich has been set in step S2. The position corresponding to the maximumES value is set to the in-focus point and the focusing lens is stoppedhere. At this time point, the photographing preparing operation iscompleted and a state in which the photographing operation can beperformed is obtained.

In step S7, a check is made to see if the second stage of the releaseswitch has been depressed or not, namely, to see if the switch (2) hasbeen turned on or not. When the switch (2) is turned on, step S8 followsand the actual exposure is executed on the basis of the iris value A_(v)and the shutter speed T_(v) which have been set in step S2. The imagesignal is recorded onto the recording medium in step S9.

A series of photographing operations are completed as mentioned above.

As described above, according to the invention, since the electroniccamera apparatus has been constructed as mentioned above, the stable andaccurate focus information without an erroneous operation can beobtained.

What is claimed is:
 1. An electronic camera comprising:a) focusdetecting frame setting means for setting a focus detecting frame intoan image sensing plane so that its size can be changed; b) focusdetecting frame size setting means for setting a size of the focusdetecting frame on the basis of a first signal component regarding ahigh frequency component extracted from an image pickup signalcorresponding to the inside of the focus detecting frame; and c) focusdetecting means for detecting a focusing state on the basis of a secondsignal component regarding an edge component extracted from the imagepickup signal corresponding to the inside of the focus detecting frameset by the focus detecting frame size setting means and for executing afocus adjustment on the basis of said focusing state.
 2. A cameraaccording to claim 1, wherein in a state in which the size of the focusdetecting frame is set to the minimum value, said focus detecting framesize setting means compares a level of the first signal component and areference level and enlarges an area of the focus detecting frame at apredetermined ratio when said first signal component level is equal toor lower than said reference level.
 3. A camera according to claim 2,wherein said first signal component is a high frequency component in theimage pickup signal and said focus detecting frame size setting meansincludes signal processing means for normalizing the high frequencycomponent on the basis of a luminance signal level and converting into asignal which is independent of a contrast.
 4. A camera according toclaim 1, further having:recording means for recording the image pickupsignal onto a recording medium.
 5. An electronic camera comprising:a)focus detecting frame setting means for setting a focus detecting frameinto an image sensing plane so that its position can be changed; b)focus detecting frame position setting means for setting a position ofthe focus detecting frame on the basis of a first signal componentregarding a high frequency component extracted from an image pickupsignal corresponding to the inside of the focus detecting frame; and c)focus detecting means for detecting a focusing state on the basis of asecond signal component frequency characteristic different from that ofthe first signal regarding an edge component extracted from the imagepickup signal corresponding to the inside of the focus detecting framewhich has been set by the focus detecting frame position setting meansand for executing a focus adjustment on the basis of said focusingstate.
 6. A camera according to claim 5, wherein in a state in which aposition of the focus detecting frame is set to the center of the imagesensing plane, said focus detecting frame position setting meanscompares a level of the first signal component and a reference level andchanges the position of the focus detecting frame by a predeterminedalgorithm until said first signal component level exceeds the referencelevel when the first signal component level is equal to or lower thansaid reference level.
 7. A camera according to claim 6, wherein saidfocus detecting frame setting means executes the focus detecting framesetting operation in a state in which a focusing lens for the focusadjustment has been located almost near the center of a moving range. 8.A camera according to claim 6, wherein said first signal component is ahigh frequency component in the image pickup signal and said distancemeasurement frame position setting means includes signal processingmeans for normalizing the high frequency component by a luminance signallevel and for converting into the signal which is independent of acontrast.
 9. A camera according to claim 5, further having:recordingmeans for recording the image pickup signal onto a recording medium.